One application for methods as stated above and the corresponding device is the sealing of bag-shaped or tubular packages, such as for instance sausages. These are frequently sealed with U-shaped closure clips made of aluminum. High demands are made on the quality of such closure. It should not be so tight that the packaging casing is damaged when sealing the same. At the same time, however, the closure should be sufficiently tight, and during processing steps subsequent to the sealing of a sausage should not slip off the same. Due to these high demands made on the closure, the extent to which the clip is compressed upon completion of the sealing operation--subsequently referred to as clip height--must precisely be achieved for the respective type of package by adjusting a corresponding sealing distance. This is first of all effected empirically. Once the corresponding parameters for a type of product have been defined, they can be adjusted on the sealing machine. In the commercially available sealing machines it is generally possible to adjust the desired sealing distance. In most cases, a scale is provided, which provides for adjusting the same value for the clip height at a later date. Such sealing machine in the form of a desk top unit is known from DE-GM 19 33 066.
When the sealing machine has been adjusted to the corresponding product, the sealing operation is performed as follows:
First of all, a portion of a tubular casing is filled with the filling--for instance sausage meat. Subsequently, the filled sausage casing is pinched by two pairs of displacement shears. The same will then move away from each other axially with respect to the axis of the sausage and thus form a casing neck free from meat, which is disposed between the stamp and the bottom tool of the sealing machine. In the bottom tool, an open closure clip has been inserted. For sealing the closure clip, stamp and bottom tool are moved towards each other, so that the casing neck free from meat is seized by the open closure clip. Subsequently, the stamp impinges on the free legs of the U-shaped closure clip, bending the same about the casing neck. For sealing the casing neck, stamp and bottom tool first of all move towards each other, where they seal the closure clip and subsequently move away from each other, in order to release the closure clip. At the turning point of their movement, stamp and bottom tool have a sealing distance from each other which is decisive for the resulting clip height. The clip height of a sealed closure clip thus results from the actual sealing distance of stamp and bottom tool at the turning point between their movements towards each other and away from each other.
Since the system of levers moving stamp and bottom tool applies forces up to 2000 kg during the sealing operation, there will necessarily occur a certain wear. The resulting clearance is not considered when setting the sealing distance by means of the scale on the sealing machine. The consequence is that the scale reading does not correspond with the actual sealing distance and accordingly not with the actually resulting clip height either. Thus, the actually resulting clip height is not the originally determined desired clip height for which the sealing distance has been adjusted on the scale. Even during a current production, the wear caused by the clearance of the system of levers leads to the fact that the sealing distance of stamp and bottom tool is constantly increasing, so that the closure clips are sealed less and less tight and for instance during the subsequent processing of a sausage may slip off the same.
Accordingly, the users of such sealing machines are forced nowadays to newly check and possibly correct the tightness of the closure with each production start. However, the testing methods are quite specific and depend on the tester and thus are very subjective. The closure clip height very frequently lies below the required height for safety reasons, i.e. the closure clips are sealed too tight. As a result, the sealing machine is subjected to a much higher mechanical load than would actually be necessary, which leads to an increased wear and thus an early failure of the machine.